Process for stripping metal from a cathode



March 17, 1970 P. M. JAS BERG 3,501,385

7 PROCESS FOR STRIPPING METAL FROM A CATHODE Filed May 8, 1967 2Sheets-Sheet 1 INVENTOR. PETER M. JHSBERG March 1970 P. M. JAS aBERG3,501,385

PROCESS FOR STRIPPING METAL FROM A CATHODE Filed May 8, 1967 2Sheets-Sheet 2 INVENTOR. PETfR IZ JRSBERG HTTYS.

United States Patent O f 3,501,385 PROCESS FOR STRIPPING METAL FROM ACATHODE Peter M. Jasberg, Kellogg, Idaho, assignor to The Bunker HillCompany, Kellogg, Idaho, a corporation of Delaware Filed May 8, 1967,Ser. No. 636,797

Int. Cl. C23b 7/08 US. Cl. 204-42 10 Claims ABSTRACT OF THE DISCLOSUREThe disclosure herein is directed to the Stripping of electrolyticallydeposited sheets from a plate cathode in metal recovery processes. It isparticularly described with respect to recovery of zinc. The sheets arestripped by application of fluid jets at the interface between sheetsurfaces. Auxiliary mechanical rapping and Wedging steps to facilitatestripping is also described.

BACKGROUND OF THE INVENTION This invention relates to a novel processfor stripping electrolytically deposited metal from a reusable cathodein electrolytic metal recovery systems such as are used in theproduction of zinc.

The conventional method of stripping sheets of zinc from a cathode ofaluminum or aluminum alloy is carried out manually, the sheet beingchipped gradually with a chisel to pry it from the aluminum surface. Thealuminum cathode, being relatively soft, also deteriorates in such useand sometimes is damaged to an extent which makes stripping moredifficult and eventually further use of the cathode is impossible. Otheralternatives previously proposed for facilitating this operation utilizerollers to deflect the metal surfaces, mechanical impaction of the metallayer or utilize mechanical or vacuum pressure gripping devices to pullthe sheets from the cathode. Besides the complicated and expensivemechanisms required for such operations, all such mechanical processesinclude the hazard of physical damage to the cathode as Well as to thesheet of metal being removed from it. In addition, many of theseprocesses are slow and consume a working period equal to or even greaterthan conventional manual chipping methods.

According to the process described below, the deposited metal layer isremoved from the cathode by hydraulic jets directed against the metallayer along the boundary between the coated and uncoated cathode areas.The use of hydraulic jets in this manner eliminates mechanical damageboth to the cathodes and to the removed sheets of deposited metal. Ithas been found to accomplish superior results in a fraction of the timerequired for manual removal of such sheets. Various equipmentalternatives and accessory process steps are described as practicaladjuncts to the basic hydraulic stripping process.

It is a first object of this invention to provide such a process whichcan be automated to effectively strip metal from cathodes in acontinuous operation.

Another object is to provide a versatile process of releasing depositedmetal sheets applicable to cathodes lowing disclosure taken togetherwith the accompanying drawings which schematically illustrate theprocess and 3,501,335 Patented Mar. 17, 1970 ice DESCRIPTION OF THEDRAWINGS FIGURE 1 is a schematic perspective view showing a portion of aconveyor assembly and progressive stripping of metal from cathodes onthe conveyor assembly;

FIGURE 2 is an end elevation view showing a cathode and the fluidnozzles prior to stripping of the metal from the cathode, progressivestripping of the metal being illustrated in dashed lines;

FIGURE 3 is a schematic sectional view taken along line 33 in FIGURE 2showing the nozzles and a typical stream pattern;

FIGURE 4 is a view similar to FIGURE 1 illustrating the use of accessoryprocess steps to facilitate stripping in a modified form of the process;

FIGURE 5 is a plan view of a device for maintaining initial separationof the metal from the cathode; and

FIGURE 6 is a fragmentary side elevation view showing the device inFIGURE 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIGURE 1 illustrates generallythe basic steps of the instant process. At the left in this drawing is atypical rectangular cathode 10 coated about most of its surface area bya zinc layer 11. The side edges of the zinc layer 11 are defined byinsulating strips 8 on the cathodes 10 which prevent accumulation ofzinc across the vertical cathode edges. The zinc layer 11 is depositedelectrolytically on the cathode 10, the deposited metal being locatedbetween strips 8 along an area bounded by a boundary line 9 formed atthe zinc-aluminum interface created on the cathode 10 at the level atwhich cathode 10 is immersed in the electrolytic bath. Along theboundary line 9 is a short area (about /2 inch) of zinc having atapering thickness leading to the constant thickness of zinc in the bulkof the zinc layer 11. The stripping of the .zinc from the aluminum isnormally found to be most difiicult along the boundary line 9.

The zinc-coated cathodes 10 are mechanically handled by a continuoustrolley conveyor shown generally at 13. Each cathode 10 is held by aclamp 12. suspended from the conveyor 13, the cathodes 10 being in avertical position.

In the area at :which the zinc layers 11 are to be stripped from cathode10, a manifold 14 is located on each side of the conveyor 13 with one ormore nozzles 15 connected to the liquid manifold 14. The nozzles 15 aredirected toward the adjacent cathode surfaces at each end of cathode 10,preferably with the central axis of each nozzle in a plane perpendiuclarto the wide cathode surface planes. The jet from each nozzle ispreferably in alignment with the boundary line 9 and is angularydirected toward the zinc layers 11. Impingement of a high pressure waterjet from the nozzles 15 on the zinc-aluminum interface (at boundary line9) breaks the bond between the deposited zinc layer 11 and the aluminumcathode 10. Further subjection of the cathode 10 to the high pressurejet permits the jeis to penetrate between the zinc layer 11 and thecathode 19 and progressively break the bond between them from top tobottom. The deposited zinc layer is removed by simply peeling the zincfrom the aluminum cathode 10, leaving separate zinc layers 11 and aclean cathode 10 as they emerge from the area between the nozzles 15 asshown to the right in FIGURE 1.

In FIGURE 2 there is illustrated the progressive removal of the zinclayers 11 by nozzles 15 at each side of the cathode 10. The threenozzles 15 are shown directed toward the solution line 9 at an angle ofapproximately 25 relative to the plane of cathode 10. Angles of 0 to 25have been found most suited to this process and individual nozzles canbe set at differing angles. As the cathode 10 moves past the nozzles 15,the zinc layers 11 initially separate from cathode 10 adjacent the upperedges of the respective layers 11. This initial position of the freeupper edges of the strips 11 is designated in FIGURE 2 by the referencenumber 11a. As movement of cathode 10 continues and subjection of thecathode 10 and zinc layers 11 to the high pressure jets from nozzle 15is maintained, the strips 11 are freed from cathode 10 to the pointillustrated by the reference numeral 11b in FIGURE 2, wherein each zinclayer 11 is almost free to fall from the cathode 10. In actual practice,this process requires handling devices (not shown) to receive the layers11 and to convey them from the the stripping area for furtherprocessing.

A typical manifold and nozzle arrangement is shown in FIGURE 3, wherethe liquid streams produced in the high pressure jets are indicated bythe numeral 16. As the cathode 10 enters the stripping area shown inFIGURE 3, it is first subjected to a straight jet from the first nozzle15a. The stream 16a from the nozzle 15a is controlled so as to bestraight, thereby insuring maximum hydraulic impact against the cathode10 and zinc layer 11. This maximum hydraulic impact created by thestraight nozzle 15a better insures freeing of the zinc layer 11 at thearea adjacent to the solution line, where the bonding forces joining thetwo sheets are found to be strongest. Following this jet, the next twojets produced by nozzles 15b and 150 are shown flat jets with a sprayangle from 25 to 80. The liquid streams from nozzles 15b and 15c aredesignated at 16b and 160 respectively. The fan-shaped configurations ofliquid streams 16b and 16c distributes the hydraulic pressure requiredto continue peeling of the zinc layer 11 along the interface until it isfinally free from contact with cathode 10.

While many variations in operating pressure are possible, it has beenfound that effective stripping of the zinc layers is best obtained byusing manifold pressures from 4000 to 6000 p.s.i. depending upon thesize and thickness of the materials being handled. After the peeling ofzinc has begun, pressure is less significant. Subsequent jets at 300-600p.s.i. (and larger volumes) could effectively continue peeling thesheet, if directed at the interface exposed initially by a high pressurejet. Many different nozzle types and arrangements have been triedexperimentally in developing this process and all have been found towork effectively in the pressure range of 4000 to 6000 p.s.i., with aflow rate of approximately 10 gallons per minute of Water.

In one typical arrangement, the three nozzles such as shown in FIGURE 3were spaced on 8-inch centers from one another and the nozzle outletswere located /8 of one inch from the surface of the cathode 10. Thearrangement successfully removed layers of zinc deposited on 24 x 36inch aluminum cathodes during periods of both eight hours and 24 hoursand left clean cathodes with no residue of zinc along the originalsolution line 9. The stripping time for each cathode was approximatelytwo seconds and at this rate, the pressure and flow rate of the waterjets caused no excessive erosion of the cathode plates or deformation ofeither the cathode plate or the zinclayer. The resultant projectedcathode life is 2-3 years.

This process does not require the use of any particular nozzle or streamconfiguration. A single nozzle operating in the pressure rangesindicated above has beenfound to be adequate, although combinations ofup to five nozzles have been used successfully. The single nozzle usedin an actual test was a Spraying Systems Co., Nozzle No. 0010, with a 0spray angle, and a 0.078 inch orifice diameter, operating at a pressureof 5500 p.s.i. and a flow rate of 10 gallons per minute. In anothertest, a Spraying System Co. flat jet No. 1510 with a 0.078 inch orificediameter and 15 spray angle performed eifective stripping of zinc at anoperating pressure of 4700 p.s.i. and flow rate of 10 gallons perminute. Many variations in selection of nozzle and jet stream patterncan be made in adapting the instant process to particular operatingconditions to obtain optimum results.

Tests also have been carried out with a modified process using jetsoperating at substantially lower pressures. Operating pressures as lowas 600 p.s.i. to 1200 p.s.i. have been used with auxiliary equipment asillustrated in FIG- URE 4 with varying degrees of success. Thisauxiliary equipment comprises a vibrating rapper device 17 formechanically loosening the bond between the zinc layers 11 at each Sideof the cathode 10. The rapper is provided with a contacting roll 18 andis supported on a movable support 20 so that it can be positionedadjacent to the cathode 10 or pulled back when necessary. Support 20 isguided by stationary frame guides 21 on the same general frameworkassembly 23 that anchors a cylinder 22 used to position the support 20and rapper apparatus 17. The use of rapping devices for this purpose hasbeen known previously in this industry and no further description of thedetails of this apparatus is believed necessary in order to understandthe inclusion of this additional step in the basic process. Theloosening of the bond between the zinc layer 11 and cathode 10 might beaccomplished by other mechanical devices, such as olfset rolls toproduce reverse bending of the zinc layers and cathode along thesolution line 9. In any event, such mechanical loosening of the bondalong solution line 9 assists, in some instances, in insuring greatereffectiveness of stripping by the hydraulic jets, particularly where thejets are utilized at pressures below the high pressure'range (4000 to6000 p.s.i.) indicated above.

One other useful accessory step in stripping the zinc by the basicprocess involves the use of mechanically positioned wedges 28 as shownin FIGURES 5 and 6. Following initial loosening of the upper edges ofeach zinc layer 11, it has been found that, in some instances, a vacuumis partially formed between the zinc layer 11 and cathode 10. Thispartial vacuum actually pulls the zinc layer 11 back toward the cathodesurface. To counteract this force, wedges 28 are positioned between thezinc layer 11 and cathode 10 at each side of the cathode. The wedges 28are fixed to lever arms 25 pivotally connected to stationary framemembers 24 by a vertical pivot shaft 27. Each lever arm 25 is biasedinwardly toward the cathode center line by a suitable spring 26 woundabout the shaft 27. A guide roll 30 on each lever arm 25 adjacent towedge 28 prevents unnecessary pressure against the cathode 10 by thewedges 28. The width of the rolls 30 is such that the inner faces ofeach wedge 28 will actually be maintained a slight distance outward fromthe surface of the cathode 10 following initial insertion of the wedges28 between the layers 11 and cathode 10. The rolls 30 will simply rollalong the surface of the moving cathode 10 and will not mar or disturbthe normally smooth cathode surface configuration. Different wedgearrangements can be utilized, and coating of the wedges with a substanceto minimize friction (such as Teflon") will lessen cathode wear.

In the process shown in FIGURE 4, the zinc layer 11 is initially rappedby the vibrating rapper 17 at each side of the conveyor 13 to loosen thezinc layers 11 along the solution line 9. The moving cathode '10 is thensubjected to the hydraulic stripping operation previously described and,when necessary, the upper edges of the partially removed zinc layers 11are mechanically held apart from the cathode 10 by the wedges 28 duringcompletion of the stripping process.

It is to be understood that the illustration in FIGURE 4 is schematic innature. The spacing between the various devices is not necessarilyaccurately portrayed. The process involved herein obviously requireselfective timing between the various steps, and the time between rappingof the solution line initiation of hydraulic stripping, mechanicalholding of the upper edge of the partially removed layers, andcompletion of the stripping operation obviously must be varied to meetoperating conditions by proper location of the devices along theconveyor 13. Such proper positioning to achieve maximum effectiveness ata particular operating pressure, flow rate and conveyor speed isbelieved to be obvious.

In actual practice, a high percentage (9099%) of all cathodes run at thehigh pressure range indicated above (4000 to 6000 p.s.i.) have beeneffectively stripped using the hydraulic Stripping process shown inFIGURE 1, with no auxiliary solution line breaking or other devicesbeing used. Where difficult stripping is encountered, rapping of theplates to break the bond at the solution line has been found to increasethe effectiveness of the process and hydraulic stripping is then moreeasily accomplished. The use of spreading wedges in conjunction with thehydraulic jets increases the effectiveness of the process and betterutilizes the available energy from the high pressure water jet insuringthat it is directed between the adjacent zinc and aluminum surfaces.

Many variations in operating conditions will depend upon the particularrequirements of an individual installation. Changes envisioned withinthe above disclosure include:

(1) Nz zlesany number of nozzles can be used.

(2) Nozzle characteristicscan be varied individually or as a group.Variations are possible in orifice size, spray pattern and spray angles,volume-pressure relationships, impingement angles and distance fromorifice to impingement point.

(3) Direction of plate travel-can be changed when related to nozzles.

(4) Fluid-water, other liquids or gases can be used, with or withoutadditives which can vary laminar flow and effectiveness of nozzlearrangement.

(5) Point of impingement-must only be along boundary line betweencathode and zinc.

(6) Stripping speedno-t restricted, although higher stripping speedsresult in less cathode wear and more effective stripping. Must alsorelate to loading and unloading rate of cathodes.

(7) Flow charcteristicsdevices to straighten flow between manifold andnozzle increase effectiveness.

Many other modifications could be made in the process without deviatingfrom the basic steps described above. The process as set out in thisdescription is practical and strips aluminum cathodes effectively whilethe cathodes are hung from the moving conveyor 13. The time involved(less than 2 seconds) is much less than the time required to manuallystrip the zinc by chisels (about 11 seconds). The process minimizes thepossibility of mechanical damage to the vulnerable cathodes. Byproviding the hydraulic stripper apparatus at two sides of the cathodeshung vertically from a conveyor, the forces exerted against the cathodealong each of its sheet faces serve to oppose and balance one another.The method described, since it eliminates manual operations, can beautomated and applied continuously in a zinc recovering process.

Having thus described my invention, I claim:

1. A process for stripping a deposited metal layer from a cathodepreviously dipped in an electrolytic solution and coated wtih depositedmetal along anarea bounded by a solution line, comprising the followingstep:

impinging a fluid jet on the cathode and deposited metal layer along anexposed interface with the jet angularly directed toward the coated areaof the cathode to thereby separate the deposited metal layer from thecathode in the form of a sheet.

2. The process as set out in claim 1 wherein the deposited metal layeris mechanically impacted along the solution line prior to impingement bythe fluid jet.

3. The process as set out in claim 1 wherein the deposited metal layeris mechanically held apart from the cathode after initial disengagementfrom the cathode.

4. The process as set out in claim 1 as applied to a flat sheet cathodewherein a series of successive fluid jets successively impinge on thesheet and deposited metal in oppositely directed streams against the twosheet faces.

5. The process as set out in claim 1 as applied to a flat sheet cathodemoving in a direction parallel to its sheet faces wherein a series ofsuccessive fluid jets successively impinge on the sheet and depositedmetal in oppositely directed streams against the two sheet faces.

6. The process as set out in claim 1 wherein the cathode and depositedmetal layer are successively impinged by a straight fluid jet and thenby a succeeding fluid jet with a widening spray angle.

7. The process as set out in claim 1 wherein the jet comprises a liquidjet and the jet pressure is between 4000 to 6000 psi.

8. The process as set out in claim 1 wherein the fluid jet to initiallybreak the bond of the deposited metal layer is a liquid jet having a jetpressure between 4000 to 6000 p.s.i., and subsequent liquid jet pressureapplied to the interface between the deposited metal layer and cathodeis above 300 psi.

9. The process as set out in claim 1 wherein the jet is directed towardthe cathode at an angle of no more than 25 degrees from the cathodesurface.

10. The process as set out in claim 1 wherein the cathode is aluminum,the metal layer is zinc and the fluid is water.

References Cited W. H. Safranek, Product Engineering, June 5, 1961, pp.609-614.

JOHN H. MACK, Primary Examiner T. TUFARIELLO, Assistant Examiner

